1. Field of the Invention
The present invention relates to a lapping tape used for lapping of the surface of a magnetic head, magnetic disk or the like.
2. Description of the Related Art
A lapping tape which has a lapping layer formed on a flexible substrate is used for the precision finish processing of a magnetic head or surface finish processing of a magnetic recording medium. The lapping layer is formed by coating a paint for the formation of a lapping layer onto a flexible substrate, followed by drying. The paint for the formation of a lapping layer contains, in the kneaded or dispersed form, inorganic powders such as aluminum oxide, chromium oxide, silicon carbide, iron oxide, silicon nitride or diamond; an organic binder such as polyvinyl chloride resin, polyester resin or polyurethane resin; and other components.
As a process for producing a lapping tape, there is a conventionally known process described in Japanese Patent Application Laid-Open No. HEI 5-192869, wherein a lapping tape is produced using a paint comprising an epoxy resin which has repeated units of a specific structural formula and has an average molecular weight of 1000 to 10000, a polyurethane resin which has a number-average molecular weight of 5000 to 20000 and has an OH group at its terminal, and a polyfunctional isocyanate. It is said that according to the above process, a sufficient crosslinking rate and also a high crosslink density can be obtained by using the above resins in combination even if the crosslinking temperature is lowered to room temperature.
Disclosed in Japanese Patent Application Laid-Open No. HEI 5-192870 is a process of producing a lapping tape which comprises using an epoxy resin which contains recurring units of a specific structural formula and has an average molecular weight of 1000 to 50000, a polyester resin which has a number-average molecular weight of 1000 to 30000, has an OH group at its terminal and has a glass transition point (Tg) of -20 to 40.degree. C., and a polyfunctional isocyanate. It is reported that the non uniformity of the qualities which occurs during the hardening reaction can be reduced by using the above resins in combination.
It is however difficult to say that the lapping tape obtained according to each of the above proposals has a sufficient coating layer strength. There happens to occur inconvenience that the coating layer as a lapping layer peels during the lapping test.
The present invention has been made in view of the foregoing situations. An object of the present invention is to provide a lapping tape which functions sufficiently with a good balance as a lapping tape upon lapping the surface of a magnetic head, magnetic disc or the like, more specifically, a lapping tape which can prevent the generation of scratches on the surface to be lapped to the utmost, has a sufficient coating layer strength, has a peeling-resistant lapping layer and has excellent lapping ability.